Why are my eyebrows falling out? My eyebrows have been falling out for over two years now.

I have naturally thick eyebrows, so it hasn't been very noticeable. They do grow back, but they keep falling, always with a white sebum plug at the end, normally be sitting on my eyebrows. They sit detached on my eyebrows, which become itchy sometimes. I thought it might be mites or dandruff, but I've used apple cider vinegar, mouthwash, tea tree oil, moisturizing, and nothing's worked. Recently, I've noticed that when my forehead gets moist I get paste all over that rubs off.